The disclosure generally relates to a method and system for determining an operational status of a steering system, and more specifically, to a method and system for determining and evaluating the operation of steering axes in a multiple-link steering system.
Steering systems are common in machines or vehicles for rotating or steering mechanical parts. For example, virtually every vehicle uses a steering system to steer the wheels. One important characteristic of a steering system is the steering axis around which mechanical parts or wheels rotate or pivot. For motor vehicles, an alignment process is used to determine and adjust parameters of the steering axis and the steering system. The parameters include camber, caster, steering axis inclination (SAI) and toe.
A camber angle is the inclination of the wheel plane viewed from the front with respect to the vertical plane. A camber angle is defined positive when the wheel leans outward at the top, and negative when it leans inward. Caster is the angle of the steering axis, viewed from the side of the vehicle, relative to the tire""s vertical centerline. A caster angle is considered positive when the top of steering axis is inclined rearward and negative when the top of the steering axis is inclined forward. Steering axis inclination (SAI) is the angle between the steering axis, when viewed from the front of the vehicle, relative to the vertical line of the vehicle.
In order to measure these parameters, an operator may use a vision imaging system such as a computer-aided, three-dimensional (3D) machine vision that employs optical sensing devices, such as cameras, to determine the positions of various objects. Examples of such apparatus and methods are disclosed in U.S. Pat. No. 5,724,743, entitled xe2x80x9cMethod and Apparatus for Determining the Alignment of Motor Vehicle Wheels,xe2x80x9d issued to Jackson, et al. on Mar. 10, 1998, and in U.S. Pat. No. 5,535,522, entitled xe2x80x9cMethod and Apparatus for Determining the Alignment of Motor Vehicle Wheels,xe2x80x9d issued to Jackson, et al. on Jul. 16, 1996, each incorporated herein by reference.
These methods and systems work properly for vehicles using conventional steering systems. In a conventional steering system, each of the front wheels is connected to a knuckle. The knuckle has two ball joints: an upper ball joint connects to an upper link and a lower ball joint connects to a lower link. A steering link is connected to the knuckle via a pivot joint. The upper and lower ball joints work as pivot points. A driver uses a steering wheel that connects to the steering link to steer, or control the pivot of, the knuckle, which in turn pivots the wheels. As a result, the wheel pivots about a fixed steering axis extending from the upper ball joint to the lower ball joint.
FIG. 1 shows a multiple-link steering system 10, a different type of steering system. In FIG. 1, a knuckle 12 is attached to the brake rotor 16 of front wheel. Knuckle 12 has three ball joints: an upper ball joint 22 and two lower ball joints 26 and 28. An upper link 27 connects to knuckle 12 via upper ball joint 22 and to the chassis via two pivot hinges, forming a rigid triangle. A front lower link 32 connects to knuckle 12 via lower ball joint 28 and to the chassis via ball joint F. A rear lower link 34 connects to knuckle 12 via lower ball joint 26 and to the chassis via ball joint R. A steering link 14 is connected to knuckle 12 via another ball joint 24. Similar to the conventional steering system, a driver uses a steering wheel that connects to steering link 14 to steer, or control the pivot of, knuckle 12, which in turn pivots the wheel.
The chassis connections, and the interconnections of the linkage elements just described, constrain the motions of those elements relative to each other and the chassis. In particular, since the wheel is rigidly attached to knuckle 12, which is attached to links 32 and 34 at joints 26, 28, and links 32 and 34 are attached to the chassis at joints F and R, joints 26, 28 are constrained to move along arcs defined by this linkage. Due to this linkage, the position of joint 26 determines the position of 28, and vice versa. These positions determine the position and orientation of knuckle 12, and the wheel attached thereto, relative to the chassis. As steering link 14 moves from one position to another, joints 26, 28 also move.
Lower links 32, 32 may be parallel to each other in space. Thus, the extension lines FL, RL of lower links 32, 34 do not necessarily intersect with each other. A pivot point may be defined as the midpoint of the two closest points on extension lines FL, RL of lower links 32, 34. Other definitions of pivot points may also be used. FIGS. 1 and 2 show an example when the extension lines of lower links 32, 34 intersect with each other. In this case, since the distance between the two lines is zero, the midpoint (the pivot point) is thus the same as the intersection point. In FIG. 1, a steering axis Xref about which the wheel pivots is defined as an axis passing through upper pivot point 22 and lower pivot point, which is the intersection 25 of lower links 32, 34.
Due to the movable linkage structure, the multiple link steering system does not have a fixed steering axis as that in conventional non-multiple-link steering systems. Rather, the multiple link steering system has a variable steering axis as the wheel turns. The change in the steering axis can be seen from FIGS. 1 and 2.
In FIGS. 1 and 2, the wheel is steered to a first direction and a second direction respectively. In FIG. 2, the steering axis of FIG. 1 is marked as Xref, and the positions of two lower links of FIG. 1 are marked as FL and RL respectively. Due to the structure of the movable linkages, when the wheel is steered from the first direction to the second direction, front lower link 32 moves from FL to line Fxe2x80x2Lxe2x80x2, and rear lower link 34 moves from line RL to line Rxe2x80x2Lxe2x80x2. As a result, the intersection of the two lower links shifts from point 25 to point 35. The steering axis hence shifts from Xref to X2, which extends from ball joint 22 to point 35, when the wheel is steered to the second direction. Accordingly, the steering axis of a multiple link steering system moves as the wheels are steered.
Other types of multiple-link steering systems are also available and have similar characteristics as illustrated in FIGS. 1 and 2. One type of multiple-link steering system has two upper links and only one lower link. Another type of multiple-link steering system has two links attached to both the upper and lower parts of the knuckle. The steering axes in these multiple-link steering systems also move as wheels are steered.
As steering axes in multiple-link steering systems move as wheels are steered, conventional methods for measuring parameters for a steering axis in non-multiple-link steering systems are not suitable for determining or evaluating steering axes in multiple link steering systems. Efforts have been devoted in establishing mathematical models for calculating the positional parameters of steering axes in a multiple-link steering system. However, such mathematical models are often complicated, and require a considerable amount of data and complex calculations. There is a need for a method and system that can easily evaluate the operation status of a multiple-link steering system, and without the need to know the exact positional parameters of the steering system. There is also a need to identify the existence of a multiple link steering system
Diagnostic methods and systems are described to determine the existence and operational status of a multiple-link steering system for steering an object attached thereto. An exemplary diagnostic system includes a position determination system and a data processing system. The data processing system is coupled to the position determination system and configured to receive and process signals sent from the position determination system.
The position determination system is configured to obtain positional signals related to the steering system. In one example, the position determination system includes an optical sensing device, such as a camera, to form a viewing path with targets attached to the object. The optical sensing device generates positional signals of the targets based on the images or signals sensed by the device. In another example, the position determination system uses non-contact methods to obtain positional signals of the steering system. For example, an optical sensing device is used to view a wheel and generates signals of the wheel positions based on the images or signals sensed by the device.
The data processing system has a data processor for processing data and a data storage device for storing data. The data storage device bears instructions upon execution by the data processor causing the data processing system to perform a diagnostic process. In one embodiment, the data processing system receives a first, second and third positional signal of the steering system when the object is being steered to a first, second and third steering angle respectively. The data processing system calculates a first positional parameter for the steering system based on the first and second positional signals, and a second positional parameter for the steering system based on the second and third positional signals. An operational status of the steering system is determined based on the first and second positional parameters, and reference positional parameters.
In another embodiment, the diagnostic system is used to determine the operational status of a steering system in a vehicle having multiple-link suspension. The data processing system calculates multiple positional parameters, such as caster values, of the steering system based on the positional signals. The data processing system has access to data related to specifications of the steering system under test. The operational status of the steering system may be determined by comparing the positional parameters and the specifications of the steering system.
In one aspect, the calculated positional parameters are evaluated to determine if the parameters are substantially the same throughout various portions of the turning and measurement process. If the values are substantially constant, it is determined that the steering system is a non-multiple-link steering system. Position determination methods corresponding to non-multiple-link steering systems will be used.
If, however, the parameters vary at different steering angles, then it is determined that the steering system is a multiple-link steering system and corresponding position determination methods can be used. For instance, in a vehicle, the method may include measurements of steering the wheel in multiple small segments of turning.
The measurement of various steering segments may be made in both steering directions. For example, from left to the right and from right to the left, or vice versa. A plot of the measurements may show hysteresis of the steering, and thus reveal further deficiencies, such as worn components, in the vehicle being measured and diagnosed. Alternatively, the process may include only one measurement at or near the straight ahead toe position, to determine the caster, SAI, and steering axis position corresponding to the straight ahead position. For example, measurements may be taken when the wheel is steered from xe2x88x924 degrees to 4 degrees.
In another embodiment, the data processing system designates the first positional parameter as the caster value corresponding to the first steering angle and the second positional parameter as the caster value corresponding to the second steering angle. In another embodiment, the data processing system designates the first positional parameter as the caster value corresponding to a steering angle between the first and second steering angle, and the second positional parameter as the caster value corresponding to a steering angle between the second and third steering angle. In still another embodiment, the first positional parameter is designated as the caster for an angle substantially equal to either the first steering angle or the second steering angle, and the second positional parameter is designated as the caster for an angle substantially equal to either the second steering angle or the third steering angle.
In still another embodiment, the diagnostic system is used to determine the operational status of a steering system of a vehicle having multiple-link suspension. The diagnostic process used by the diagnostic system measures multiple caster values of the vehicle at different steering angles in small increments. For example, caster measurement is taken every 5 degrees, spanning a +/xe2x88x9220xc2x0 range relative to the thrust line of the vehicle.
Still other advantages of the diagnostic system and method will become readily apparent from the following detailed description, simply by way of illustration and not limitation. As will be realized, the method and system are capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.